Evershed, John

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Evershed, John

(b. Gomshall, Surrey, England, 26 February 1864; d. Ewhurst, Surrey, England, 17 November 1956)

solar physics.

The seventh son of John EverShed and Sophia, daughter of David Brent Price of Portsmouth, Evershed came of a family long established in Surrey and was educated at a private Unitarian school in Brighton and later at Croydon. In 1906 he married Mary Acworth Orr, who assisted him in his work until her death in 1949. A year later Evershed married Margaret Randall, who survived him; there were no children form either marriage.

Evershed was introduced into scientific circles by his elder brother Sydney, an inventor of electrical apparatus for the Royal Navy and a researcher in permanent magnetism. As a young man he studied solar spectroscopy and carried out experiments in the production of continuous and absorption spectra of heated gases at his private observatory at Kenley, Surrey. He was fortunate in inheriting in 1894 the instruments of A. Cowper Ranyard, the distinguished amateur astronomer; these included an eighteen-inch refractor and a spectrograph. A liberal-minded employer (he was engaged in the analysis of oils and other products for a London firm) granted him leave to go on several total solar eclipse expeditions. Professor H. H. Turner provided introductions which led him in 1898 to travel for this purpose to India via the United States (where Evershed spent a month with George E. Hale) and Japan. It was on this expedition that he photographed for the first time the continuous spectrum to the ultraviolet of the Balmer series limit at λ 3646.

Correspondence and meetings with Sir William Huggins, then president of the Royal Society, resulted in Evershed’s appointment as assistant to C. Michie Smith, director of the Kodaikanal and Madras observatories in India. Making full use of the high altitude of Kodaikanal (2,343 meters) and of his skill in designing and building instruments, Evershed began a long series of spectroheliograms of the sun’s disk. He further began the research which led in 1909 to the discovery in sunspots of the small radial motions of gases parallel to the sun’s surface, now known as the Evershed effect. In 1911 he succeeded to the directorship of the Kodaikanal and Madras observatories. During his period of office he carried out a great deal of chromospheric research, made early use of hydrogen α spectroheliograms, and, in 1915, led an expedition to Kashmir, where exceptionally good viewing conditions made it possible for him to measure the small shift to the red of spectrum lines in connection with Einstein’s predictions.

Evershed retired in 1923 and returned to England. He settled at Ewhurst, Surrey, where with undiminished enthusiasm he again equipped a private observatory. There he carried out high-dispersion work (employing large liquid prisms) to determine the exact wavelengths of the solar spectrum, sunspots, prominences, and minute line-shifts, and to study the Zeeman effect in assessing the strength of magnetic fields of sunspots. The death of his wife deprived him of her practical assistance, but he continued to make observations until 1953. He then presented some of his instruments to the Royal Greenwich Observatory.

An ingenious designer of optical instruments and an indefatigable and meticulous observer, Evershed contributed much to the knowledge of solar physics during the early decades of this century.

BIBLIOGRAPHY

F. J. M. Stratton, “John Evershed,” in Biographical Memoirs of Fellows of the Royal Society (1957) contains a full bibliography of Evershed’s work. Some representative examples are “Experiments on the Radiation of Heated Gases,” in Philosophical Magazine, 39 (1895), 460; “Wave-length Determinations and General Results Obtained From a Detailed Examination of Spectra Photographed at the Solar Eclipse of January 22, 1898,” in Philosophical Magazine, 39 (1895),460; “Wave-length Determinations and General Results Obtained From a Detailed Examination of Spectra Photographed at the Solar Eclipse of January 22, 1898,” in Philosophical Transactions of the Royal Society, 197A (1901), 381; “Solar Eclipse of 1900 May 28—General Discussion of Spectroscopic Result,” ibid., 201 (1903), 457; “Radial Motions in Sunspots,” in Monthly Notices of the Royal Astronomical Society, 70 (1910), 217; “The Spectrum of Nova Aquilae,” ibid., 79 (1919), 468; “The Solar Rotation and Shift Towards the Red Derived From the H and K Lines in Prominences,” ibid., 95 (1935), 503; “Note on the Zeeman Effect in Sunspot Spectra,” ibid., 99 (1939), 217; and “Measures on the Relative Shift of the Line 5250.218 and Neighboring Lines in Mt. Wilson Solar Magnetic Field Spectra,” ibid., 99 (1939), 438.